The present invention relates generally to wireless networks and more specifically to a hierarchical architecture for wireless networks.
In large campus or metropolitan networks, a “distributed” context transfer protocol can be used to directly transfer context from an “old AP” to a “new AP”, when a MN roams. The IEEE 802.11f draft protocol, for example, defines a distributed context transfer protocol. However, there are a number of inherent problems with such a distributed approach. A secure context transfer requires a many-to-many trust relationship between APs (or requires some additional hierarchy). In addition, a protocol is needed to enable the “new AP” to determine the “old AP” when a MN roams, the “old AP” 802.11 Reassociation field is not sufficient. Context is passed around from AP to AP as a station roams; therefore, critical context may be lost (e.g. if the link to an old AP is lost). Furthermore, a distributed protocol is susceptible to an inherent race condition where “handoff messages” for rapidly roaming stations may arrive out-of-order.
Thus, a need exists for a network protocol and topology that is capable of supporting a large number of infrastructure nodes that enables mobile nodes to roam seamlessly within a single subnet or between a plurality of subnets in a campus network. The path between each mobile node and correspondent host (CH) should be reliably re-established when the mobile node roams. Because the campus network may include a large population of stations that roam frequently, the so overhead for roaming should be minimal.